A Spitz (5-years old, castrated male) and a Maltese (9-years old, castrated male) were presented with weight loss, polyuria/polydipsia (PU/PD) and depression. Diabetic ketosis was diagnosed based on clinical signs, physical examinations and screening tests (CBC, serum chemistry and urinalysis). The dogs were treated with NPH initially. However, NPH was inadequate to control blood glucose level due to the short duration of the action (< 5 hours). Because of the poor glycemic control with NPH, the dogs showed diabetic complications including weight loss and cataract. After change to glargine, the duration of insulin action was extended up to 11 hours. As a result, there was significant improvement in clinical signs and serum fructosamine concentrations. This study suggests that glargine is useful as a long-acting insulin in dogs which have poor glycemic control due to the short duration of NPH.